Ure electromagnet operating arm retaining means in a vehicle brake struct

ABSTRACT

An electromagnet assembly for use in vehicle brakes having an operating arm in which the magnet housing is held on said arm by an attachment and retaining means consisting of a pair of holes spaced from the axial center pole of the magnet and a pair of fingers on the operating arm extended into the holes in the center pole. A round plastic keeper means is attached to the outer end of the finger in the hole nearest the trailing edge of the operating face of the magnet and forms a force transmitting means between the magnet and the finger and arm. The other finger and holes serve as an anti-rotational means, and the hole having the keeper means is provided with either a pair of opposed shoulders or an annular shoulder near the end of the hole opposite the operating face of the magnet to provide a restriction for the keeper means to retain the magnet in place on the fingers.

Grove Sept. 4, 1973 ELECTROMAGNET OPERATING ARM RETAINING MEANS IN AVEHICLE BRAKE STRUCTURE Leroy K. Grove, 512 S. Merrifield Ave.,Mishawaka, Ind. 46544 Filed: Nov. 10, 1971 Appl. No; 197,308

Inventor:

References Cited UNITED STATES PATENTS 5/1964 Birge 188/138 4/1966 Birge188/138 X 4/1966 Brede et al. 188/138 11/1969 Hubbard 188/164 PrimaryExaminer-Ge0rge Harris Attorney-Marmaduke A. Hobbs et a1.

[57] ABSTRACT An electromagnet assembly for use in vehicle brakes havingan operating arm in which the magnet housing is held on said arm by anattachment and retaining means consisting of a pair of holes spaced fromthe axial center pole of the magnet and a pair of fingers on theoperating arm extended into the holes in the center pole. A roundplastic keeper means is attached to the outer end of the finger in thehole nearest the trailing edge of the operating face of the magnet andforms a force transmitting means between the magnet and the finger andarm. The other finger and holes serve as an anti-rotational means, andthe hole having the keeper means is provided with either a pair ofopposed shoulders or an annular shoulder near the end of the holeopposite the operating face of the magnet to provide a restriction forthe keeper means to retain the magnet in place on the fingers.

17 Claims, 15 Drawing Figures PATENTEDSEP'MQB 3.757. 264

SHEET 1 or 3 INVENTOR. 1E 20) A. GROVE 5 7 ATTORNEYS PATENTEDSEP 4191asum 2 or 3 1N VENTOR.

I LEROY KGIPOI E ATTORNEYS PATENTEDSEP 41 1 3.151. 284

sum 3 0f 3 I N VEN TOR.

ZERO) A. s ans J B' 31 g ATTORNEYS ELECTROMAGNET OPERATING ARM RETAININGMEANS IN A VEHICLE BRAKE STRUCTURE In a conventional, hydraulicallyactuated brake, a pair of brake shoes are pivotally secured to astationary brake back-up plate and are moved into contact with a brakedrum by the actuation of a piston in a hydraulic brake cylinderresponsive to fluid pressure applied to the brake cylinder. In anelectrically actuated system, the brake shoes are moved by meansresponsive to an electrical current, such a system being exemplified bythe U.S. Fat. to William F. Penrose, No. 2,273,065. In theseelectrically operative systems, a lever arm is pivotally secured to thebrake back-up plate such that rotation of the lever arm causes movementof the brake shoes into contact with the brake drum. At the end of thelever arm is secured an electromagnet which is usually maintained insliding contact with an armature plate which is secured to and moveswith the brake drum. In a one piece cast iron drum and hub assembly, theface of the drum may serve as the armature plate. When the electromagnetis energized, it is magnetically attracted to the rotating armatureplate, and, due to the friction between these two metal parts soattracted, a force is imposed on the magnet tending to move it in thedirection of movement of the armature. This force is in turn transmittedby the lever arm to actuate the brake shoes into braking engagement witha brake drum.

In the present state of the art, brake electromagnets are generallyattached to the brake shoe actuating arm as described in Us. Pat. Nos.2,273,065 or 3,244,259. As set forth in the first of these patents, itis desirable to mount the electromagnet non-rigidly on the lever armfrom within the central portion of the electromagnet and at a planeclosely adjacent that of the rubbing contact between armature andelectromagnet in order to reduce the moments tending to overturn theelectromagnet. This relationship helps to prevent the establishment ofunequal presures on the face of the electromagnet and hence helps togreatly minimize the production of localized high temperature and highpressure areas. It is also desirable to mount the electromagnet so thatit has limited freedom of axial and universal pivotal movement withrespect to the lever arm. If the armature in rotating tends to oscillateslightly in the axial direction due to end play, or to wobble orotherwise run out of true, the electromagnet can move in accommodationtherewith, thereby tending to maintain the desired flat rubbing contactrelationship between the electromagnet and armature faces. The momentstending to tip or overturn the magnet produce unequal pressures on theface of the magnet, and the resulting high pressure and high temperatureareas of the magnet face are extremely detrimental to the brakingperformance and useful life of the magnet.

In operation, the brake electromagnet is mounted on the brake actuatingarm and is maintained in a light pressure contact with the armatureplate or drum face by spring pressure. When the electric brakes areapplied, the magnet is energized and is magnetically attracted to therotating armature. The magnet moves with the rotating armature untilrestrained by the brake actuating arm. The drum armature continues torotate and generates extreme surface friction and heat at the face ofthe magnet. The tilting moments created at the point of restraint of themagnet by the actuating arm impose an increased contact pressure on theleading edge of the magnet, i.e. the edge meeting the oncoming armatureface, and a corresponding reduction of pressure on the trailing edge.This of course increases the friction and wear on the leading edge ofthe magnet. As the leading edge wears down, it forms a new taperedfriction face plane from the leading edge to the point of actuating armrestraint, and in a relatively short time the trailing half of themagnet is not in contact with the armature. Hence, the brakingeffectiveness of the mag net is continuously reduced until completefailure occurs.

The present state of the art, in actual practice and as set forthhereinbefore, does not recognize another important factor of the magnetmounting design which also determines the magnitude of the momentstending to tilt or overturn the magnet toward its leading edge. Thisfactor is the distance of the restraining force from the leading edge ofthe magnet. The moments of tilt imposed by the restraining force arereduced in direct proportion to an increase in the distance of therestraining force from the leading edge. Thus there are three basicdesign objectives in the mounting of the electromagnet to the actuatingarm which must be achieved to improve the performance and extend theuseful life of the electromagnet, namely: minimizing the distance of therestraining force from the frictional face of the magnet to reducetilting moments, maximizing the distance of the restraining force fromthe leading edge of the magnet to reduce tilting moments, and minimizingthe frictional locking tendency of the magnet on the actuating lever armto insure that the magnet has the necessary freedom of movement requiredto maintain its full face in flat rubbing contact with the armatureface.

In current practice, two basic systems of mounting the electromagnet onthe actuating lever arm are employed. One system utilizes a pin or studattached to the actuating lever arm and extending into a round hole inthe center of the magnet core. The pin or stud has a spherical headwhich restrains the magnet while permitting sufficient universalmovement of the magnet face. Another pin or projection extends from theactuating lever arm into and through an outboard lugor projection whichprotrudes from the outer periphery of the magnet near the side oppositethe friction face. This is used to prevent rotation of the magnet andhas a restraining clip or pin to retain the magnet on the actuatinglever arm. While unnecessary tilting moments are created by the locationof the restraining force and the anti-rotational lug, one of the majordisadvantages of this system is the expensive construction of theactuating lever arm and the magnet.

The other mounting system in use employs a rectangular restraining arminserted in a rectangular hole in the core of the magnet. Therectangular restraining arm in a rectangular hole prevents rotation ofthe magnet and also serves to retain the magnet on the lever arm by useof a retaining pin through a hole in the arm and an accommodating slotrecessed in the face of the magnet core. This system is less expensive;however, to gain this advantage the tilting moments were increased bymoving the point of the lever arm restraining force considerably closerto the leading edge of the magnet, and replacing the smooth sphericalsurface which restrained the lever arm by sharp steel edges which tendto lock the magnet in one position when subjected to the restraining andtwisting forces imposed on the magnet.

It is therefore one of the principal objects of the present invention toprovide a magnet and lever arm attachment means which will greatlyincrease the performance and useful life of the electromagnet, and whichis relatively simple in construction and operation, resulting in optimumperformance of the magnet and arm in the braking operation.

In the present invention, the object of increasing the performance anduseful life of the electromagnet by improving and simplifying theattachment, retention and operating relationship of the electromagnet tothe brake actuating arm is accomplished by: applying the restrainingforce as close to the magnet friction face as possible, thus reducingthe tilting moments; moving the restraining force away from the leadingedge of the magnet as far as operating clearances permit, much fartherthan is current practice, thus further reducing the tilting moments;restraining the magnet by a spherical bushing of plastic with arelatively low coefficient of friction, such as nylon, thus avoidingfrictional lockup.

Further objects and advantages of the present invention will becomeapparent from the following description and accompanying drawings,wherein: I

FIG. I is an elevational view of a backing plate, brake shoe andoperating mechanism of the type which may be used in combination with myelectromagnet attachment and retaining device;

FIG. 2 is a cross-sectional view of an electromagnet embodying thepresent invention, the section being taken on line 22 of FIG. 1;

FIG. 3 is an elevational view of the operating lever arm of the brakeshown in the preceding figures;

FIG. 4 is an edge elevational view of the lever arm shown in FIG. 3, asviewed from the position indicated by line 4-4;

FIG. 5 is a fragmentary edge elevational view of the lever arm;

FIG. 6 is an exploded perspective view of an electromagnet and theattachment device for securing the magnet to the lever arm;

FIG. 7 is a plan view of a portion of the attachment device shown inFIG. 6;

FIG. 8 is a cross-sectional view of the part shown in FIG. 7, thesection being taken on line 8-8 of the last figure;

FIG. 9 is a cross-sectional view of a modified form of the parts shownin FIGS. 7 and 8;

FIG. 10 is a plan view of the part shown in FIG. 9;

FIG. 11 is a plan view of the magnet;

FIG. 12 is an elevational and fragmentary crosssectional view of themagnet .shown in FIG. 11,

FIG. 13 is a fragmentary cross-sectional view taken on line 13 13 ofFIG. 12; and

FIGS. 14 and 15 correspond to FIGS. 11 and 12 but illustrate a modifiedform of the attachment structure.

Referring more specfically to the drawings and FIG. I in particular,numeral 10 indicates generally the brake assembly, including a brakeoperating mechanism l2 and a brake drum 14 which is attached to andnormally forms a part of the wheel structure of the vehicle in which thebrake is used. The brake assembly includes a backing plate 16 on whichbrake shoes 18 and 20 are pivotally mounted and movably secured theretoor restrained by spring-loaded retaining pin assemblies 22 and 24,respectively. The brake shoes contain friction material 26 and 28 bondedto the external surface of the brake shoes, and engage the internalsurface of drum 14 when the brake is applied. An adjustment screw 30interconnects the brake shoes, which are yieldably retained in theirretracted position from the brake drum by springs 32 and 34.

The brake actuating mechanism for applying brake shoes 18 and 20 intobraking engagement with the drum consists of an electromagnet 40, alever 42 connected at one end to the magnet and pivotally mounted on apin 44, which in turn is secured to backing plate 16. Lever 42 swings onpin 44 and is curved in an offset manner to pass around the drum axisand to position the electromagnet at a point 1180 degrees from pin 44.Arm 42 includes an extension or short arm 46 carrying a pin 48 on aswivel block 50, which bears against the adjacent ends of the brakeshoes. The magnet is operated in conjunction with a radially positionedarmature 51 connected directly to or forming an integral part of brakedrum 14, on a plane parallel with backing plate 16. The magnet 40 isadapted to frictionally engage the face of the armature when energizedand is mounted on arm 42 by an attachment and retainer means 55described more fully hereinafter. A coil spring 57 reacting betweenlever 42 and the magnet urges the magnet into light pressure contactwith the armature.

The magnet attachment and retainer means 55, best shown in F IGS. 2 and6, consists of finger 60 and finger 62 joined integrally at a rightangle to lever 42 and extending into holes 64 and 66, respectively, inthe center pole of magnet 40. A force transmitting bushing 70, which issecured to the end of finger 60 and retains the magnet on the fingers,fits freely in hole 64 with only the spherical diameter of the bushingcontacting the cylindrical wall of the hole as near as practical to thefrictional face of the magnet. This design minimizes tilting momentswhile permitting smooth, friction free, limited universal movement ofthe magnet. The two holes 64 and 66 are offset in opposite directionsfrom the axis of the center pole 68, with hole 64 being offset in the direction of the trailing edge of the magnet housing for minimizing unevenwear of the magnet face as explained hereinbefore.

Round restraining hole 64 is located off center toward the trailing edgeof the magnet, thus permitting the anti-rotational hole 66 to be in thecenter core rather than on the outer periphery of the magnet as in somepresent brakes. Bushing 7t) and finger 60 transmit the force createdbetween the armature and the magnet to arm 42 for actuation of thebrake, while finger 62, in round hole 66, prevents any substantialrotation of the magnet on its center axis. The two fingers 60 and 62 arepreferably formed as an integral part of the actuating lever 42, andadded strength is gained at the right angle bend by web 79 connectingthe two fingers. The

'upper end of finger 60, as viewed in FIGS. 2, 4 and 6,

contains a pair of opposed slots 72 and 74 which grip the inner wall 76of bushing when the bushing is pressed onto the free end of finger 60,in the manner illustrated in FIG. 2, thus releasably locking the bushingin place on the end of finger 60. In order to retain the magnet 40 onfingers 60 and 62 when the brake drum and armature are not in place,shoulders 77 and 78, as shown in FIG. 11, are provided at the lower edgeof hole 64 which require the compression of ribs 82 and 84 of bushing'70, as shown in FIGS. 7 and 8, in order for it to pass between theshoulders. This relationship retains the magnet on the fingers while atthe same time permitting the magnet to be disassembled from the fingersby forcing the magnet away from lever 42 and forcing bushing 70 throughthe lower end of hole 64 between the two shoulders 77 and 78.

A modification of the hole is illustrated in FIGS. 14 and 15, whichconsists of a single annular shoulder 80 for retaining the magnet on thetwo fingers, the hole defined by shoulder 80 being large enough topermit finger 60 to easily pass therethrough, but being sufficientlyrestricted to prevent bushing 70, or a modified form of bushing 70 asshown in FIGS. 9 and 10, from slipping from hole 64, thus retaining themagnet on the fingers and requiring removal of the bushing from aportion having a spherical diameter near the upper end, i.e. adjacentthe friction face of the magnet. Both bushings 70 and 70 are preferablymade of low friction, high density plastic material.

In a simple and rapid assembly operation, compression spring 57 isaffixed to the lever arm encircling the two upright fingers which serveas a guide to maintain the spring in a central concentric positionagainst the magnet. The magnet is placed over the two fingers so thatthe two fingers extend through their mating holes in the magnet. Theplastic drive bushing 70 or 70' is pressed into position over the end offinger 60, completing the assembly operation of the magnet and am. Asmentioned previously, the plastic drive bushing serves to retain themagnet to the lever arm as well as transmit the braking force from themagnet to arm 42. As previously mentioned, the round hole 64 in themagnet is restricted at the end opposite the friction face to preventpassage of the drive bushing and this restriction may take the form of asmaller round hole-or protruding flat shoulders. To disassemble themagnet from the actuating arm, the arm is held down with one hand and afirm jerk on the magnet releases it from the acutating arm.

In positioning the plastic restraining and force transmitting bushing ina relatively close position to the face of the magnet and hence close tothe armature, and in offsetting restraining hole 64 and finger 60 towardthe trailing edge of the magnet face, tilting moments are minimal anduneven wear of the contact surface of the magnet is eliminated orminimized so that the full effectiveness of the magnet face is alwaysavailable for the braking operation. Further, by locating theantirotational hole 66 and finger 62 in the center pole of theelectromagnet rather than in an outboard peripheral lug, both the magnetand actuating arm are simplified and less expensive to fabricate. Thenew plastic force transmitting bushing 70, or 70, with its low frictionspherical restraining surface, smoothly transmits the force createdbetween the armature and the magnet to arm 42 to actuate the brake. Thisbushing also assures a smooth, friction free, limited universal movementof the magnet which is necessary to maintain its flat, rubbingrelationship with the drum armature. Finally this force transmittingbushing 70 serves to retain the magnet on the actuating arm when thebrake drum and armature are not in place.

While only one embodiment of the present magnet and arm structure hasbeen described in detail herein,

together with several modifications, various other changes andmodifications may be made without departing from the scope of theinvention.

I claim: t

1. An electromagnet assembly for use in electric vehicle brakes havingan operating arm, comprising a housing having a center pole and aperipheral pole and an annulus therebetween, said center pole having apair of holes, fingers on the actuating arm each extending into one ofthe holes in said center pole, and retaining means secured to one ofsaid fingers for transmitting the force from said magnet to said arm andfor retaining the magnet on said fingers.

2. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which said holes in said center pole are bothround and are spaced from the axial center of the housing of saidelectromagnet.

3. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which said hole receiving said retaining means isoffset from the center axis of said pole in the direction correspondingto the trailing edge of the face of said housing.

4. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 3 in which the other of said fingers serves as ananti-rotational means for the magnet and the hole therefor is offsetfrom the center axis toward the leading edge of the face of the housing.

5. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which said retaining means has a spherical portionand said spherical portion contacts the cylindrical wall of the hole inclose proximity to the friction face of the magnet.

6. An electromagnet assembly for use in electric vehicle brakes asdefined in claim I in which a coil spring reacts between said magnet andsaid arm for urging said magnet away from said arm into operatingposition.

7. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 5 in which said hole receiving said retaining means islarger than said other hole and said other hole is offset from the axialcenter of said coil of said center pole in the direction toward saidforward edge of the magnet housing.

8. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 7 in which the finger receiving the retaining means islarger than the other of said fingers.

9. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which fingers are joined integrally to theoperating arm.

10. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which a web interconnects said fingers adjacentthe lever arm.

1 1. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which said retaining means is round and contains ahole therein for receiving the respective finger and said fingercontains a recess for receiving and securing said retaining means whenplaced on the end of one of said fingers adjacent the operating face ofthe magnet.

12. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which said hole for receiving said retaining meanshas a pair of opposed shoulders near the end of the hole opposite theoperating face of the magnet.

13. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which said hole for hicle brakes as defined inclaim 1 in which the hole receiving said retaining means has opposedshoulders near the end thereof spaced from the friction face of themagnet and said retaining means is provided with opposed yieldablebosses for passing between said shoulders.

17. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 13 in which the-hole receiving said retaining means hasan annular shoulder forming a restriction therein in spaced relation tothe friction face of the magnet.

l l l

1. An electromagnet assembly for use in electric vehicle brakes havingan operating arm, comprising a housing having a center pole and aperipheral pole and an annulus therebetween, said center pole having apair of holes, fingers on the actuating arm each extending into one ofthe holes in said center pole, and retaining means secured to one ofsaid fingers for transmitting the force from said magnet to said arm andfor retaining the magnet on said fingers.
 2. An electromagnet assemblyfor use in electric vehicle brakes as defined in claim 1 in which saidholes in said center pole are both round and are spaced from the axialcenter of the housing of said electromagnet.
 3. An electromagnetassembly for use in electric vehicle brakes as defined in claim 1 inwhich said hole receiving said retaining means is offset from the centeraxis of said pole in the direction corresponding to the trailing edge ofthe face of said housing.
 4. An electromagnet assembly for use inelectric vehicle brakes as defined in claim 3 in which the other of saidfingers serves as an anti-rotational means for the magnet and the holetherefor is offset from The center axis toward the leading edge of theface of the housing.
 5. An electromagnet assembly for use in electricvehicle brakes as defined in claim 1 in which said retaining means has aspherical portion and said spherical portion contacts the cylindricalwall of the hole in close proximity to the friction face of the magnet.6. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 1 in which a coil spring reacts between said magnet andsaid arm for urging said magnet away from said arm into operatingposition.
 7. An electromagnet assembly for use in electric vehiclebrakes as defined in claim 5 in which said hole receiving said retainingmeans is larger than said other hole and said other hole is offset fromthe axial center of said coil of said center pole in the directiontoward said forward edge of the magnet housing.
 8. An electromagnetassembly for use in electric vehicle brakes as defined in claim 7 inwhich the finger receiving the retaining means is larger than the otherof said fingers.
 9. An electromagnet assembly for use in electricvehicle brakes as defined in claim 1 in which fingers are joinedintegrally to the operating arm.
 10. An electromagnet assembly for usein electric vehicle brakes as defined in claim 1 in which a webinterconnects said fingers adjacent the lever arm.
 11. An electromagnetassembly for use in electric vehicle brakes as defined in claim 1 inwhich said retaining means is round and contains a hole therein forreceiving the respective finger and said finger contains a recess forreceiving and securing said retaining means when placed on the end ofone of said fingers adjacent the operating face of the magnet.
 12. Anelectromagnet assembly for use in electric vehicle brakes as defined inclaim 1 in which said hole for receiving said retaining means has a pairof opposed shoulders near the end of the hole opposite the operatingface of the magnet.
 13. An electromagnet assembly for use in electricvehicle brakes as defined in claim 1 in which said hole for receivingsaid retaining means has an annular shoulder near the end of the holeopposite the operating face of the magnet.
 14. An electromagnet assemblyfor use in electric vehicle brakes as defined in claim 1 in which saidretaining means is constructed of low friction, high density material.15. An electromagnet assembly for use in electric vehicle brakes asdefined in claim 14 in which said retaining means has a peripheralportion with a spherical diameter.
 16. An electromagnet assembly for usein electric vehicle brakes as defined in claim 1 in which the holereceiving said retaining means has opposed shoulders near the endthereof spaced from the friction face of the magnet and said retainingmeans is provided with opposed yieldable bosses for passing between saidshoulders.
 17. An electromagnet assembly for use in electric vehiclebrakes as defined in claim 13 in which the hole receiving said retainingmeans has an annular shoulder forming a restriction therein in spacedrelation to the friction face of the magnet.